Two Photon Absorption

A nonlinear image technique for characterization of the optical nonlinearities is used to investigate the solid semiconductor ZnSe at 600 nm. The method based on a 4f nonlinear image technique with a phase object is used to obtain the diffraction pattern of the nonlinear filter in solid ZnSe located at the Fourier plane by a CCD camera. The nonlinear absorption coefficient and nonlinear refraction index were both obtained by fitting the nonlinear image. Good agreement between the experiment data and the simulated result are obtained indicating a sensitive and powerful method for nonlinear optical measurements.

We report the measurements of the third-order susceptibilities and two-photon absorption in three different polymers doped with p-phenyl sydnone moiety viz., 2-benzylhydrazono-5-(3-p-tolylsydnone-4-yl)1,3,4,-thiadiazine, which is recently synthesized and characterized, with the prospective of reaching a good compromise between processability and high nonlinear optical properties. The measurements were done using nano second Z-scan at 532nm. The Z-scan spectra reveal a large negative nonlinear refraction coefficient n2 of the order 10−14 cm2/W and a two-photon absorption β, which is determined to be the order of cm/GW. The absorption cross section is 10−46 cm4 s/photon. The molecular second-order hyperpolarizability in PMMA matrix was calculated to be 1.47 × 10−31 esu, comparable with stilbazolieum derivatives, a well-known class of optical materials for photonics and biophotonics applications. The chromophore shows its optical power limiting behavior in all the three polymer matrices. All these results suggest that this moiety has potential for the application of all-optical limiting and switching devices. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

We use the real (Kerr) and imaginary (two photon absorption) parts of a third order optical nonlinearity to tune the long (1.6μm) and short wavelength (1.3μm) band edges of a stop gap in a two-dimensional silicon photonic crystal. From pump-probe reflectivity experiments using 130fs pulses, we observe that a 2μm pulse induces optical tuning of the 1.3μm edge via the Kerr effect whereas a 1.76μm pulse induces tuning of the 1.6μm band edge via both Kerr and Drude effects with the latter related to two-photon induced generation of free carriers with a lifetime of ˜900ps .

“All Nobel Laureates did not understand how the atom absorbs a photon”
Adrian Ferent

“In Ferent Quantum Gravity the photon is absorbed by the atom as a dipole”
Adrian Ferent

“In Ferent Quantum Gravity the photon is absorbed by the dipole not by the electron”
Adrian Ferent

“In Ferent Quantum Gravity the photon is absorbed by the dipole not by the electron, the interaction between atom and photon has greater probability than the interaction between electron and photon”
Adrian Ferent

“The photon is absorbed by the atom not by the electron”
Adrian Ferent

Two-photon absorption measurement has been carried out in a single 80 nm×10 μm ZnO nanowire using femtosecond laser pulses in the wavelength range of 700-800 nm. In addition to the deep-level green emission around 530 nm due to surface defects and the near band-edge ultraviolet emission around 360 nm due to the exciton, a second harmonic peak has been observed. The strength of the frequency-doubled component is found to enhance while the two-photon absorption wavelength is tuned towards the exciton wavelength of the nanowire. This behavior can be ascribed to the resonant exciton absorption in ZnO nanowires.

A series of 2,6- and 2,7-bis(styryl)anthracene derivatives with the donors at the styryl group and acceptors at the 9,10-positions have been synthesized, and their two-photon cross sections (Φδmax) were determined. These compounds exhibit a peak two-photon absorptivity (δmax) in the range of 700–2500 GM at 780–1030 nm. Values of λmax and Stokes shifts increase as the acceptor is changed to a stronger one. There is also a parallel increase in and δmax with the same variation of the chromophore structure. Both and Φδmax have been optimized by introducing donor-substituted styryl groups at the 2,6-positions and p-cyanophenyl groups at the 9,10-positions, respectively. The effect of a π center on the two-photon absorption properties has been assessed by comparing the existing data for a variety of D–π–D derivatives.

Stationary ultrashort light pulses of 10-psec duration and with an energy of 10 μJ per pulse were obtained from an active--passive mode-locked Nd:YAG laser by using a two-photon absorption limiter (GaAs) inserted into the resonator. The stability of energy in the steady-state part of the pulse train, containing approximately 90 pulses, is better than {plus minus}1.5%. The dynamics of the pulse-shortening mechanism are described, and it is shown that maximum pulse compression is reached after only approximately 10 round trips.